Energy transfer and kinetics in mechanochemistry

Harnessing Nature's Ingenuity: A Comprehensive Exploration of Nanocellulose from Production to Cutting-Edge Applications in Engineering and Sciences

Primary material supply is the heart of engineering and sciences. The depletion of natural resources and an increase in the human population by a billion in 13 to 15 years pose a critical concern regarding the sustainability of these materials; therefore, functionalizing renewable materials, such as nanocellulose, by possibly exploiting their properties for various practical applications, has been undertaken worldwide. Nanocellulose has emerged as a dominant green natural material with attractive and tailorable physicochemical properties, is renewable and sustainable, and shows biocompatibility and tunable surface properties. Nanocellulose is derived from cellulose, the most abundant polymer in nature with the remarkable properties of nanomaterials. This article provides a comprehensive overview of the methods used for nanocellulose preparation, structure-property and structure-property correlations, and the application of nanocellulose and its nanocomposite materials. This article differentiates the classification of nanocellulose, provides a brief account of the production methods that have been developed for isolating nanocellulose, highlights a range of unique properties of nanocellulose that have been extracted from different kinds of experiments and studies, and elaborates on nanocellulose potential applications in various areas. The present review is anticipated to provide the readers with the progress and knowledge related to nanocellulose. Pushing the boundaries of nanocellulose further into cutting-edge applications will be of particular interest in the future, especially as cost-effective commercial sources of nanocellulose continue to emerge.

The Effect of Mechanical Activation of Fly Ash on Cement-Based Materials Hydration and Hardened State Properties

Fly ash from coal represents the foremost waste product of fossil fuel combustion. These waste materials are most widely utilised in the cement and concrete industries, but the extent of their use is insufficient. This study investigated the physical, mineralogical, and morphological characteristics of non-treated and mechanically activated fly ash. The possibility of enhancing the hydration rate of the fresh cement paste by replacing part of the cement with non-treated and mechanically activated fly ash, and the hardened cement paste's structure and early compressive strength performance, were evaluated. At the first stage of the study, up to 20% mass of cement was replaced by untreated and mechanically activated fly ash to understand the impact of the mechanical activation on the hydration course; rheological properties, such as spread and setting time; hydration products; mechanical properties; and microstructure of fresh and hardened cement paste. The results show that a higher amount of untreated fly ash significantly prolongs the cement hydration process, decreases hydration temperature, deteriorates the structure and decreases compressive strength. Mechanical activation caused the breakdown of large porous aggregates in fly ash, enhancing the physical properties and reactivity of fly ash particles. Due to increased fineness and pozzolanic activity by up to 15%, mechanically activated fly ash shortens the time of maximum exothermic temperature and increases this temperature by up to 16%. Due to nanosized particles and higher pozzolanic activity, mechanically activated fly ash facilitates a denser structure, improves the contact zone between the cement matrix, and increases compressive strength up to 30%.

Spiers Memorial Lecture: Mechanochemistry, tribochemistry, mechanical alloying - retrospect, achievements and challenges

The paper presents a view on the achievements, challenges and prospects of mechanochemistry. The extensive reference list can serve as a good entry point to a plethora of mechanochemical literature.

Efficiency and Prospects of the Use of Mechanochemical Treatment to Obtain Innovative Composite Systems

This review is devoted to the possibilities of using mechanochemical processing and to achievements in this field for obtaining materials for a wide range of purposes. The mechanochemical processing of various materials and compositions in energy-intensive grinding devices allows the production of innovative systems, ensuring the necessary complex structure and properties. A detailed analysis of the processes of mechanochemical processing in the production of designs for various purposes is given, and the latest practical results in this area are highlighted. A detailed analysis of the processes of mechanochemical processing in the production of structures for various purposes is given, as well as recent practical results in this area, such as the use of mechanochemical processing to increase the performance of aluminum and other metals used as a combustible substance in energy-intensive systems. This review also presents the prospects for the use of mechanochemical processing to obtain physiologically active drugs from plant materials, which is an effective method for creating new materials in the field of pharmaceuticals, animal husbandry, veterinary medicine, crop production, etc.

Mechanochemical debromination of waste printed circuit boards with marble sludge in a planetary ball milling process

An effective management of waste printed circuit board (WCB) recycling presents significant advantages of an economic, social, and environmental nature. This is particularly the case when a suitable valorisation is made of the non-metallic parts of the WCBs, well known for their "hidden" toxicological risks. Such benefits motivate research on techniques that could contribute to mitigating their adverse socio-environmental impacts. In this work, waste printed circuit boards (WCBs) containing tetrabromobisphenol A (TBBPA) as a brominated flame retardant (BFR) underwent debromination using a mechanochemical treatment (MCT) and marble sludge, another recoverable waste, as well as pure CaO as additives. All runs in this work were performed at an intermediate rotation speed of 450 rpm, using additive/WCB mass ratios (R_m) of 4:1 and 8:1, ball to powder ratios (BPR) of 20:1 and 50:1, treatment times from 2.5 h to 10 h, two WCB sizes (powder and 0.84 mm) and marble sludge, from original to precalcined conditioning. Stainless steel jars and balls were used to verify the effect of each parameter on the system and to seek an optimum process. Complete debromination of 0.84 mm WCBs was achieved at 450 rpm, using a R_m of 8:1, a BPR of 50:1, a residence time of 10 h (more than 95% in only 5 h), and a precalcined marble sludge as additive. The results revealed that when using a R_m of 4:1 instead of 8:1, more waste could be effectively treated, per batch with a lesser need for additives, at the expense of a slightly lower level of debromination efficiency. In the same way, an appropriate apparent ball diameter (with respect to the volume of the used jar) should be carefully studied in relation to WCB size in order to achieve a beneficial total amount of energy transfer during milling.

Horizontal planetary mechanochemical method for rapid and efficient remediation of high-concentration lindane-contaminated soils in an alkaline environment

Lindane is a persistent organic pollutant that has attracted worldwide attention because of its threat to human health and environmental security. A horizontal planetary mechanochemical method was developed for rapid and efficient degradation of lindane in soil in an alkaline environment. Under the condition of a very low reagent-to-soil ratio (R = 2%), ball-to-powder ratio (C_R = 6:1), rotation speed (r = 300 rpm) and high soil single treatment capacity (S_C = 60 g), the lindane in four typical soils (~ 100 mg/kg) can be degraded up to 96.30% in 10 min. This method can also remediate high-concentration lindane-contaminated soil (833 ± 26 mg/kg). The experimental results and theoretical calculations proved that the stepwise dechlorination and final carbonization of lindane in soil are mainly attributed to the combined action of mechanical energy and alkalinity. The bimolecular elimination (E2) reaction was the first step of lindane destruction. Subsequently, the unimolecular elimination (E1) reaction tended to occur with the weakening of alkalinity. Then, benzene was obtained through stepwise hydrogenolysis reaction. The last was the generation of carbon substances by fragmentation or condensation of benzene rings. This work proposes a practical remediation technology for organic contaminated soil and improves the understanding of the degradation pathways of lindane in soil in alkali-assisted mechanochemical system.

Experiments and modeling of mine soil inertization through mechano-chemical processing: from bench to pilot scale using attritor and impact mills

Mechano-chemical treatment has been recognized to be a promising technology for the immobilization of heavy metals (HMs) in contaminated soils without the use of additional reagents. Despite this, very few studies aiming to investigate the applicability of this technology at full scale have been published so far. In this study, a quantitative approach was developed to provide process design information to scale-up from laboratory- into pilot-scale mechano-chemical reactors for immobilizing heavy metals in contaminated mining soil. In fact, after preliminary experiments with laboratory-scale ball mills, experiments have been carried out by taking advantage of milling devices suited for pilot-scale applications. The experimental data of this work, along with literature ones, have been quantitatively interpreted by means of a mathematical model allowing to describe the effect of milling dynamics on the HM immobilization kinetics for applications at different scales. The results suggest that the mechanical process can trigger specific physico-chemical phenomena leading to a significant reduction of HMs leached from mining soils. Specifically, after suitably prolonged processing time, HM concentration in the leachate is lowered below the corresponding threshold limits. The observed behavior is well captured by the proposed model for different HMs and operating conditions. Therefore, the model might be exploited to infer design parameters for the implementation of this technique at the pilot and full scale. Moreover, it represents a valuable tool for designing and controlling mechano-chemical reactors at productive scale.

Mechanochemical degradation of brominated flame retardants in waste printed circuit boards by Ball Milling

Degradation of brominated flame retardants (BFRs) in waste printed circuit boards (WPCBs) occurred due to mechanical force during the crushing process. In this study, a planetary ball-milling simulation experiment was designed to explore the mechanochemical debromination process of BFRs in WPCBs. The results showed that CaO had a better debromination performance than MgO and the mixture of Fe + SiO₂, and high revolution speed and low mass ratio of WPCBs to CaO promoted the degradation of BFRs. After milling for 1 h, the particle size distribution was stable while the debromination efficiency increased with the increase of milling time. Ball milling promoted the migration of bromine from the inside to the new surface of WPCBs powder, and submicron particles adhered to the micron size aggregates. The polybrominated diphenyl ethers (PBDEs) detection showed that the concentrations of most PBDE congeners decreased with the increase of milling time, and a possible degradation pathway was proposed according to the experimental results. All the results provided new data for the mechanism of degradation of BFRs in WPCBs during the mechanical crushing process.

Mechanochemical stabilization of heavy metals in fly ash with additives

Mechanochemistry, as a non-thermal method showing remarkable degradation for persistent organic pollutants, is extended to stabilize the heavy metals in municipal solid waste incineration (MSWI) fly ash in the present study. The leaching suppression of heavy metals (i.e., Zn, Pb, Cu, Cr, Cd, and Ni) facilitated by five additives during mechanochemical (MC) treatment is systematically investigated, identifying that almost all heavy metals are effectively suppressed with the assistance of either CaO or Ca₃(PO₄)₂. The pH-dependent leaching test further reveals the superiority of Ca₃(PO₄)₂ over CaO for heavy metals stabilization. Moreover, the evolution of heavy metal speciations analysed via an optimized sequential extraction procedure shows that MC treatment with Ca₃(PO₄)₂ significantly reduces the water- and acid-soluble fraction with high mobility from 56.8, 1.39, 12.3, 8.46, 1.13, and 29.5% to 4.96, 0.17, 0.14, 7.36, 0.12, and 0.22%, respectively for Cd, Cr, Cu, Ni, Pb, and Zn. The risk assessment indicates remarkable detoxification of fly ash in terms of heavy metals after MC treatment: the Nemerow pollution index is dramatically decreased from 9.35 (far above 3.0- the threshold of seriously polluted domain) to 0.71 (slightly over 0.7- the threshold of safety domain). Finally, a hypothetical mechanism according with results in this study for MC stabilization of heavy metals in fly ash is proposed as: the conversion of heavy metal compounds from mobile to immobile form through reaction with additives after activated by mechanical energy.

Degradation of endosulfan by high-energy ball milling with CaO: process and mechanism

Mechanochemical degradation (MCD) technology has shown its remarkable potential in the disposal of persistent organochlorines in a non-combustion manner. In the present study, endosulfan, as the newly listed persistent organic pollutants (POPs) in the Stockholm Convention, was investigated for its feasibility of mechanochemical destruction using high-energy ball milling. Using calcium oxide (CaO) as a co-milling reagent, the degradation efficiency of endosulfan was nearly 100% after ball milling for 60 min, while the dechlorination efficiency and the sulfate formation efficiency were delayed for endosulfan degradation. After ball milling for 120 min, the dechlorination efficiency and sulfate formation efficiency reached 87.55% and 26.28%, respectively. Based on the measurement results from various material characterization approaches, the main degradation pathway of endosulfan was proposed as sequential dechlorination followed by the destruction of hydrocarbon skeleton. The GC-MS analysis confirmed that complete desulfurization and dechlorination had been realized finally. This study provides an option for the way toward the efficient and rapid destruction of endosulfan as a new POPs using mechanochemical technology.

Mechanochemical degradation of PCDD/Fs in fly ash within different milling systems

Two distinct mechanochemical degradation (MCD) methods are adopted to eliminate the polychlorinated dibenzo-p-dioxins and -furans (PCDD/Fs) from fly ash in municipal solid waste incinerators. First, experiments are conducted in a planetary ball mill for selecting suitable additives, and an additive system of SiO₂-Al is chosen for its high-efficiency, low-price, and good practicability. The I-TEQ value of PCDD/Fs in washed fly ash decreases dramatically from 6.75 to 0.64 ng I-TEQ/g, after 14 h of milling with 10 wt % SiO₂-Al, and dechlorination is identified as the major degradation pathway. Then, this additive is applied in a horizontal ball mill, and the results indicate that the degradation of PCDD/Fs follows the kinetic model established in planetary ball mills. However, longer milling time is required for the same supplied-energy because of the lower energy density of horizontal ball mills, resulting in partial loss of Al reactivity and a lower degradation efficiency of PCDD/Fs. During MCD, the evolution of PCDD/F-signatures is analogous, indicating a similar acting mechanism of all additives in both the two milling systems. Finally, a major dechlorination pathway of PCDD-congeners is proposed based on the signature analysis of congeners synthesized from chlorophenols.

Highly-effective mechanochemical destruction of hexachloroethane and hexachlorobenzene with Fe/Fe3O4 mixture as a novel additive

In this study, Fe/Fe₃O₄ mixture was first applied as an additive to achieve the highly-effective mechanochemical destruction (MCD) of two halogenated organic pollutants (HOPs), hexachloroethane (HCE) and hexachlorobenzene (HCB). The MCD of HCE was more effective than that of HCB in virtue of the lower dissociation energy of CCl bond. The MCD of HOPs occurred mainly via the reduction by Fe, Fe₃O₄ and Fe/Fe₃O₄. The oxidation of Fe₃O₄ and reduction of FeO (formed on account of the oxidation of Fe by oxygen-containing species) may also contribute to the HOP destruction. Fe/Fe₃O₄ mixture exhibited a higher dechlorination rate (DR) than other three effective additives (i.e., Fe/SiO₂, Al/Al₂O₃ and Mg/Al₂O₃ mixture), owing to the electrical property of Fe₃O₄ and its electron transfer with Fe. The HOP destruction was significantly impacted by the mass fraction of Fe₃O₄ (MF_mag) and achieved the maximum level with an MF_mag of 70%. The DR of HOPs in the atmosphere of air was higher than those of pure oxygen and nitrogen because of the oxygen vacancy in Fe₃O₄ and oxidation of Fe. The presence of water dramatically inhibited the HOP destruction due to the decrease of collision energy and its competition for the active sites in both Fe and Fe₃O₄. As expected, the DR of HOPs increased with rotation speed, and the mass ratio of ball to reactant and additive to pollutant. The analysis of intermediates indicates that HCB destruction was mainly via dechlorination and polymerization, while HCl cleavage also played an important role in HCE destruction. The results demonstrate that Fe/Fe₃O₄ mixture is a suitable additive for MCD process.

Mechanical activation of fly ash from MSWI for utilization in cementitious materials

In the present study, the physicochemical characteristics of municipal solid waste incineration fly ashes (FA) from circulating fluidized bed (CFB) or grate furnaces are studied in detail. It is identified that the CFB FA, containing high amount of Si and Al, has better potential and properties for utilization than the grate FA, which is much richer in chlorides. Mechanical activation (MA) allows amending the properties of CFB FA, thus preparing for its subsequent utilization in cementitious materials. Compared to simple water washing, MA treatment of CFB FA further reduces the residual amount of chlorine in fly ash from 0.72 to 0.33 wt%, giving the possibility of doubling the capacity of cement kiln for fly ash disposal. The improvement in chlorine removal relates to the conversion of FA compounds from a crystalline to an amorphous state, increasing the solubility of sparingly soluble chlorides. During the curing of mortars, traces of aluminum or other nonferrous metals in CFB FA are oxidized, liberating lots of hydrogen gas; this would cause expansion problems and significantly reduce the flexural and compressive strength. MA treatment of CFB FA solves such expansion problems by exhausting these reactions in advance, respectively enhancing flexural and compressive strength from 5.7 and 35.3 MPa to 9.1 and 56.9 MPa, which is comparable to the performance of Ordinary Portland Cement. Finally, an innovative pre-treatment technique for CFB FA, combining wet ball milling and counter-current two-stage water washing, is proposed for facilitating its recycling.

Mechanochemical enhancement of the natural attenuation capacity of soils using two organophosphate biocides as models

Mechanochemical treatment by high energy ball milling is a promising technology to safely destroy organic pollutants in contaminated soil and allow its possible beneficial reuse. The present study investigates the mechanochemical activation of four major soil components, which induces generation of electrons on particle surfaces. Such phenomenon is demonstrated to occur on oxides by formation of trapped electrons in oxygen vacancies (following a zeroth-order kinetics), as well as on quartz and clayey materials to form fresh electron-rich surfaces by homolytic bond rapture (according to a first-order kinetics). Two toxic organophosphate biocides (i.e. chlorpyrifos and glyphosate) are used as model pollutants. Results show that the aromatic structure of chlorpyrifos determines a faster degradation rate, compared to the aliphatic one of glyphosate, because of the higher stability of generated radical intermediates. Moreover, the aromatic moiety facilitates adsorption on clays, thus temporarily sequestering the molecule and delaying its degradation. The many heteroatoms in both organophosphates have analogous fate: mineralization to inorganic form.

Evolution of PCDD/F-signatures during mechanochemical degradation in municipal solid waste incineration filter ash

Mechanochemical degradation (MCD) is employed for the dechlorination of polychlorinated dibenzo-p-dioxins (PCDD) and -furans (PCDF) in filter ashes from municipal solid waste incinerators, respectively with the assist of six additive systems. The evolution of PCDD/F-signatures in all eleven samples are systematically monitored and studied at the level of individual congeners, and special attention is paid to CP-route congeners, 2,3,7,8-substitution, 1,9-substitution, and 4,6-PCDF. The PCDD/F-isomers distribution follows an analogous pattern, indicating the similar acting mechanism for all additives: additives transfer electrons to attack the CCl bond and then expulse chlorine. MC dechlorination is not favored for the chlorine on β-position (2,3,7,8-position). The oxygen with stronger electronegativity in PCDD/Fs negatively influences CCl bond to accept donated electrons, hindering the removal of chlorine on 1,9-position for PCDD, and chlroine on 4,6-position for PCDF. Finally, two fair dechlorination pathways for PCDD and PCDF are respectively proposed based on the detailed analysis of CP-route congeners. The evolution of PCDD-signatures is clear, yet obscure for PCDF-signatures, which still requires further investigations.

Mechanochemical treatment of fly ash and de novo testing of milled fly ash

Mechanochemical (MC) treatment has been widely proposed to degrade chlorinated organics in various matrix materials. In this study, fly ash from municipal solid waste incineration was grinded without any addition, using an all-dimensional planetary ball mill. The treated fly ash samples were characterised using X-ray diffraction, Raman spectra, scanning electron microscopy and X-ray energy-dispersive spectroscopy. The residual content of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) was monitored, as well as polycyclic aromatic hydrocarbons (PAH), a potential precursor of PCDD/F and amorphous carbon or graphite. Finally, de novo formation experiments were performed to test the chemical reactivity of the treated fly ash. The PCDD/F in milled samples was compared to those resulting from de novo tests on these same samples. The results suggest that both milling as well as de novo tests significantly alter the PCDD/F signature, suggesting substantial differences in the mechanisms of formation and destruction.

Mechanochemical pre-treatment for viable recycling of plastic waste containing haloorganics

Chemical recycling technologies are the most promising for a waste-to-energy/material recovery of plastic waste. However, 30% of such waste cannot be treated in this way due to the presence of halogenated organic compounds, which are often utilized as flame retardants. In fact, high quantities of hydrogen halides and dioxin would form. In order to enabling such huge amount of plastic waste as viable feedstock for recycling, an investigation on mechanochemical pre-treatment by high energy ball milling is carried out on polypropylene containing decabromodiphenyl ether. Results demonstrate that co-milling with zero valent iron and quartz sand ensures complete debromination and mineralization of the flame retardant. Furthermore, a comparative experiment demonstrates that the mechanochemical debromination kinetics is roughly proportional to the polymer-to-haloorganics mass ratio.